With the advancement of technology, electronic devices with versatile functionalities haven been developed. The electronic devices with versatility have been catered to people to fulfill their desires. Nowadays the electronic devices have gradually become a basic appliance to enrich people's lives.
The electronic products today are made up of various electronic components. The required voltages applied to electronic components are different with each other. As a result, the utility power source can not satisfy all requirements of different electronic devices. In order to supply suitable voltage to ensure the normal operation of the electronic devices, a power converter is required to convert an AC power such as utility power into a voltage tailored to power the electronic devices.
With the increase of the power consumption of electronic devices and the diversity of the applications for electronic devices, a redundancy power supply system is provided to increase the reliability of power supply and meet the operating requirement of fault tolerance. The redundancy power supply system is built by connecting a plurality of power supplies in parallel and thereby supplying power to electronic devices. The configuration of the redundancy power supply system is able to prevent the interruption of power supplying to electronic devices as a result of a faulty power supply or a malfunctioned power supply, thereby ensuring the uninterrupted operation of the electronic devices.
FIG. 1 is a schematic diagram showing a redundancy power supply system according to the prior art. As shown in FIG. 1, the redundancy power supply system 1 includes a plurality of power supplies, each of which has substantially the same configuration with one another. The redundancy power supply system 1 is made up by connecting the power supplies 10 in parallel. The power supplies receive the input voltage Vin and generate an output current Io′ and a rated output voltage Vo′ accordingly in order to power the systematic circuitry of an electronic device (not shown).
As shown in FIG. 1, each power supply 10 includes a power converter 101 and an output protection circuit 102. The power converter 101 is configured to receive the input voltage Vin and generate an intermediate output voltage Vo1′ according to ON/OFF operations of an switch circuit of the power converter 101 (not shown). The output protection circuit 102 is made up of a plurality of diodes D that consist of an ORing circuit. The diodes D are respectively connected between the output terminal of the power converter 101 and the output terminal of the power supply 10 for limiting the flowing direction of the output current Io′ flowing through the output protection circuit 102, thereby prohibiting a reverse current, for example, prohibiting the reverse current flowing from normally-operating power supply to abnormally-operating power supply as a result of the short-circuiting occurred to the abnormal power supplies, or prohibiting the reverse current flowing from abnormally-operating power supply to normally-operating power supply as a result of the high intermediate output voltage Vo1′ generated by the abnormal power supplies.
However, the diodes D are well known as having a great conducting voltage drop Vt with a voltage level of, for example, 0.7V, and thus causing conduction loss which is significant. FIG. 2 is a schematic diagram showing another kind of redundancy power supply system according to the prior art. Referring to FIG. 2, the power supply 20 of the redundancy power supply system 2 of FIG. 2 employs a plurality of power transistors M to replace the diodes D of FIG. 1 to constitute the output protection circuit 102. As is well known in the art, power transistors M is featured in terms of low conducting impedance and low conducting voltage drop, using power transistors M to constitute the output protection circuit 102 can reduce the power loss of the power supply 20 and the redundancy power supply system 2 and increase the overall power efficiency. Nonetheless, the power transistor M is a bidirectional element and requires a control circuit 203 to control the switching of the power transistors M.
The control circuit 203 of the power supply 20 includes a comparator (not shown) for determining the magnitude of the output current Io′ by the comparator, thereby issuing a control signal Vs′ to control the power transistors M to turn on or off simultaneously. The comparator is configured to compare the voltage difference between the output voltage Vo′ and the intermediate output voltage Vo1′ (Vo′−Vo1′) with a first reference voltage and a second reference voltage, thereby determining the magnitude and direction of the output current Io′. When the voltage difference is lower than the second reference voltage, the control circuit 203 generates a control signal having an enable state to control the power transistors M to turn on simultaneously. When the voltage difference is higher than the first reference voltage, the control circuit 203 generates a control signal having a disable state to control the power transistors M to turn off simultaneously.
Generally, the first reference voltage is a positive voltage representing that a reverse current is flowing into the power supply and that power transistors M are required to be turned off simultaneously. The second reference voltage is set to zero representing that no reverse current is flowing into the power supply and that power transistors M can be turned on simultaneously. In other words, the control circuit 203 of the power supply 20 is allowed to compare the voltage difference between the output voltage Vo′ and the intermediate output voltage Vo1′ with the second reference voltage in order to control the power transistors M to turn on in case that no reverse current is flowing into the power supply 20. Alternatively, the control circuit 203 is allowed to compare the voltage difference between the output voltage Vo′ and the intermediate output voltage Vo1′ with the first reference voltage in order to control the power transistors M to turn off in case that a reverse current is flowing into the power supply 20.
Nonetheless, the industry has imposed strict requirements on the energy-saving capability of electric appliances. Hence, how to elevate the power efficiency of a power supply has been a major goal for the research and design engineers to pursue. A straightforward solution to elevate the power efficiency of a power supply can be achieved by increasing the number of the power transistors M. As the power transistors are electrically connected in parallel, the overall conducting impedance of the power transistors M that is the impedance of the output protection circuit 102 will be reduced with the increase of the number of the parallel-connected power transistors M. In this manner, the power loss incurred as the output current Io′ flows through the output protection circuit 102 will be lessened, and thus the power efficiency of the power supply 20 is enhanced.
Although the aforesaid solution is able to elevate the power efficiency of the power supply 20, the voltage difference between the output voltage Vo′ and the intermediate output voltage Vo1′ will be higher than the first reference voltage only if a sufficiently large reverse current is flowing into the power supply 20 due to the reduction of the impedance of the output protection circuit 102 caused by increasing the number of the parallel-connected power transistors M, given that the first reference voltage is unchanged. This would cause the control circuit 203 to control the power transistors M to turn off only if a sufficiently large reverse current is flowing into the power supply 20. In this manner, the power supply is unable to accurately prohibit the reverse current, which results in the damage inflicted on the internal electronic components of the power supply 20 due to the large reverse current.
Nevertheless, the aforesaid solution can be remedied by setting the first reference voltage at a lower voltage to eliminate the incapability of accurately detecting the reverse current with more power transistors and less power loss. However, the settable range of the first reference voltage depends on the input offset voltage of the comparator. If it is desired to set the first reference voltage at a lower voltage, the comparator of the control circuit 203 has to possess a small input offset voltage and higher manufacturing cost. In this manner, this would result in a higher manufacturing cost of the power supply 20.
Therefore, it is needed to develop a power supply that can obviate the aforesaid drawbacks lingered in the prior art. The invention is proposed to satisfy these needs.